This invention relates to inertial sensor assemblies.
It is known to micro-machine solid-state inertial sensing devices from monolithic blanks of material such as silicon. Such sensing devices may take the form of oscillating `tuning-forks` demonstrating detectable resonance when subjected to rotational accelerations (a form of solid-state rate gyro) or `spatula` cantilevered masses demonstrating detectable displacements when subjected to translation accelerations (a form of solid-state accelerometer). The material blanks into which such devices are micro-machined are also known to be treated to incorporate the integral analogue and/or digital electrical driving, sensing, processing and signalling devices necessary to render such blanks, on completion, active solid-state inertial sensing devices or `chips`.
These previous devices are micro-machined from essentially two-dimensional planar material blanks so that their resultant tuning forks and spatulas lie in the plane of the material. Since the resultant tuning-fork rate gyro senses rotation about its axis of symmetry, and since the resultant spatula accelerometer senses acceleration normal to its plane of symmetry, an array of such devices micro-machined from a planar blank of material is typically incapable of sensing rotations about more than two axes, or accelerations in more than one.
To sense rotations about three orthogonal axes, two such planar array devices are assembled into a three-dimensional form. To sense accelerations in three orthogonal axes three devices are similarly assembled. If inertial effects are to be measured precisely, the assemblies must be accurately orthogonal in alignment. Since planar array devices are small, it is difficult and costly to make and maintain accurate orthogonal alignment during assembly.
Inertial sensor assemblies are often used in aircraft and missiles, which are subject to high acceleration forces and vibration. It is important that any assembly including planar array devices be assembled in such a way that the accuracy of alignment is maintained during use despite these acceleration and vibration forces. Because the inertial sensor assemblies provide output signals to the navigational and flight control systems of the aircraft or missile, failure of the assembly during a high-force maneuver could have adverse consequences.